Independence Day sale is live!

Get Discount
Data Structures and Algorithms
Menu

Low-Level Design (LLD) Interview Questions and Solutions

Suppose you’re gearing up for tech interviews and want to stay ahead with expert tips, free DSA resources, and the latest updates on mastering design patterns, sign up for our newsletter today. In that case, it’s your gateway to unlocking premium courses and personalized guidance that can transform your preparation.

Introduction to Low-Level Design

Hey there, fellow coder! If you’ve ever felt overwhelmed by the thought of designing software systems from scratch during an interview, you’re not alone. Low-Level Design (LLD) is that crucial phase where high-level ideas turn into actionable code. Unlike High-Level Design (HLD), which focuses on the big picture like system architecture and scalability, LLD dives into the nitty-gritty: classes, methods, interfaces, and how everything interacts.

In simple terms, LLD is about creating modular, maintainable code that adheres to principles like SOLID (Single Responsibility, Open-Closed, Liskov Substitution, Interface Segregation, and Dependency Inversion). It’s where you apply design patterns—those reusable solutions to common problems—to make your code elegant and extensible. According to a 2024 survey by Stack Overflow, over 70% of developers report that understanding design patterns significantly boosts their problem-solving skills in interviews.

Why does this matter? In today’s job market, companies like FAANG (Facebook, Apple, Amazon, Netflix, Google) aren’t just testing your ability to write algorithms—they want to see if you can build real-world software that’s easy to update and scale. As one expert puts it, “LLD isn’t about reinventing the wheel; it’s about using proven patterns to solve problems efficiently.” If you’re brushing up on data structures alongside this, check out our comprehensive DSA courses to solidify your foundations.

Why LLD is Important in Interviews

Picture this: You’re in an interview, and the recruiter says, “Design a parking lot system.” Without LLD skills, you might sketch a basic class or two, but interviewers are looking for more—they want to see how you handle edge cases, apply patterns like Factory or Strategy, and ensure your design is testable.

Why LLD is Important in Interviews

Statistics from Interviewing.io show that candidates who demonstrate strong LLD principles are 2.5 times more likely to receive offers from top tech firms. It’s not just about coding; it’s about showing experience. For instance, in a 2025 report, 85% of hiring managers emphasized that LLD rounds help assess a candidate’s ability to contribute to production code right away.

LLD also ties into broader skills. If you’re into web development, understanding LLD can help you design robust backends—explore our web development courses for hands-on projects that blend these concepts.

How to Prepare for LLD Interviews

Preparation doesn’t have to be daunting. Start by mastering OOP basics in languages like Java or C++. Then, dive into design patterns: Creational (e.g., Singleton), Structural (e.g., Adapter), and Behavioral (e.g., Observer).

How to Prepare for LLD Interviews

Practice with UML diagrams—class, use-case, and sequence—to visualize your designs. Resources like GitHub repos with awesome LLD examples are goldmines. Aim to solve 5-10 problems weekly, focusing on requirements gathering, core classes, and trade-offs.

For a structured approach, our Master DSA, Web Dev, and System Design course covers LLD in depth, with mock interviews. If data science intrigues you, see how LLD applies there via our data science courses. Short on time? Try our crash course for quick wins.

Actionable advice: Record yourself solving a problem, then review for clarity. Remember, interviewers value communication—explain your choices!

Top 30 LLD Interview Questions and Solutions

Based on real interviews from companies like Amazon, Google, and Microsoft, here are 30 high-quality LLD questions. Each includes requirements, key classes, design patterns, and code snippets (in Java for consistency). These were sourced from actual experiences shared on platforms like GeeksforGeeks and Medium. We’ll break them down step-by-step.

1. Design a Parking Lot System

Requirements: Multiple floors, spots for cars/bikes, entry/exit points, fee calculation.

  • Key Classes: ParkingLot (Singleton), Floor, Spot (with types), Vehicle, Ticket.
  • Patterns: Factory (for spots), Strategy (for fees).
  • SOLID: Single Responsibility (Spot handles availability). Solution: Use a 2D array for spots. On entry, find nearest free spot; on exit, calculate fee based on time. Code Snippet:

java

				
					public class ParkingLot {

   private static ParkingLot instance;

   private List<Floor> floors;

   // Singleton getter

   public static ParkingLot getInstance() { ... }

}

This design scales to 1000+ spots, with O(1) availability checks via heaps.

2. Design a Movie Ticket Booking System (like BookMyShow)

Requirements: Movies, shows, seats, booking, payments.

  • Key Classes: Movie, Theater, Show, Seat, Booking, User.
  • Patterns: Observer (for notifications), Singleton (booking manager).
  • SOLID: Open-Closed (add payment methods without changes). Solution: Lock seats during booking to prevent conflicts. Use a state machine for seat status (available, booked, locked).

3. Design a Vending Machine

Requirements: Products, inventory, payment, dispense item.

  • Key Classes: VendingMachine (Singleton), Item, Inventory, Coin, Payment.
  • Patterns: State (idle, selecting, dispensing).
  • SOLID: Dependency Inversion (payment via interface). Solution: Handle exact change; use Strategy for coin validation. Inventory updates in real-time.

4. Design an Elevator System

Requirements: Multiple elevators, floors, requests, optimization.

  • Key Classes: Elevator, Floor, Request, Controller.
  • Patterns: Command (for requests), Strategy (scheduling algorithm).
  • SOLID: Interface Segregation (separate user/elevator interfaces). Solution: Minimize wait time with nearest elevator assignment. Simulate with priority queues.

5. Design a Snake and Ladder Game

Requirements: Board, players, dice, snakes/ladders.

  • Key Classes: Game, Board, Player, Cell (with jumps).
  • Patterns: Builder (for board setup).
  • SOLID: Liskov Substitution (cells interchangeable). Solution: Turn-based; handle wins when reaching 100. Random dice rolls for fairness.

6. Design a Tic-Tac-Toe Game

Requirements: 3×3 board, two players, win detection.

  • Key Classes: Game, Board, Player, Cell.
  • Patterns: Strategy (AI vs human).
  • SOLID: Single Responsibility (Board checks wins). Solution: Check rows/columns/diagonals after moves. Add undo with Memento pattern.

7. Design an ATM Machine

Requirements: Accounts, withdraw/deposit, PIN validation.

  • Key Classes: ATM (Singleton), Account, Card, Transaction.
  • Patterns: State (authenticated, selecting action).
  • SOLID: Open-Closed (add transaction types). Solution: Handle insufficient funds; log transactions for auditing.
This design scales to 1000+ spots, with O(1) availability checks via heaps. 2. Design a Movie Ticket Booking System (like BookMyShow) Requirements: Movies, shows, seats, booking, payments. Key Classes: Movie, Theater, Show, Seat, Booking, User. Patterns: Observer (for notifications), Singleton (booking manager). SOLID: Open-Closed (add payment methods without changes). Solution: Lock seats during booking to prevent conflicts. Use a state machine for seat status (available, booked, locked). 3. Design a Vending Machine Requirements: Products, inventory, payment, dispense item. Key Classes: VendingMachine (Singleton), Item, Inventory, Coin, Payment. Patterns: State (idle, selecting, dispensing). SOLID: Dependency Inversion (payment via interface). Solution: Handle exact change; use Strategy for coin validation. Inventory updates in real-time. 4. Design an Elevator System Requirements: Multiple elevators, floors, requests, optimization. Key Classes: Elevator, Floor, Request, Controller. Patterns: Command (for requests), Strategy (scheduling algorithm). SOLID: Interface Segregation (separate user/elevator interfaces). Solution: Minimize wait time with nearest elevator assignment. Simulate with priority queues. 5. Design a Snake and Ladder Game Requirements: Board, players, dice, snakes/ladders. Key Classes: Game, Board, Player, Cell (with jumps). Patterns: Builder (for board setup). SOLID: Liskov Substitution (cells interchangeable). Solution: Turn-based; handle wins when reaching 100. Random dice rolls for fairness. 6. Design a Tic-Tac-Toe Game Requirements: 3x3 board, two players, win detection. Key Classes: Game, Board, Player, Cell. Patterns: Strategy (AI vs human). SOLID: Single Responsibility (Board checks wins). Solution: Check rows/columns/diagonals after moves. Add undo with Memento pattern. 7. Design an ATM Machine Requirements: Accounts, withdraw/deposit, PIN validation. Key Classes: ATM (Singleton), Account, Card, Transaction. Patterns: State (authenticated, selecting action). SOLID: Open-Closed (add transaction types). Solution: Handle insufficient funds; log transactions for auditing.

8. Design a Library Management System

Requirements: Books, members, borrow/return, fines.

  • Key Classes: Library, Book, Member, Loan.
  • Patterns: Observer (overdue notifications).
  • SOLID: Dependency Inversion (database interface). Solution: Track due dates; calculate fines daily.

9. Design a Car Rental System

Requirements: Vehicles, reservations, users, payments.

  • Key Classes: RentalSystem, Vehicle, Reservation, User.
  • Patterns: Factory (vehicle types).
  • SOLID: Interface Segregation (user/admin views). Solution: Availability calendar; integrate with maps for locations.

10. Design a Chess Game

Requirements: Board, pieces, moves, rules.

  • Key Classes: Game, Board, Piece (abstract), Player.
  • Patterns: Flyweight (shared piece types).
  • SOLID: Liskov (pieces extend base). Solution: Validate moves; detect checkmate with recursion.

11. Design a Splitwise-like Expense Sharing System

Requirements: Groups, expenses, settlements.

  • Key Classes: User, Group, Expense, SplitStrategy.
  • Patterns: Strategy (equal/unequal splits).
  • SOLID: Open-Closed (new split types). Solution: Graph for debts; simplify settlements.

12. Design a Stack Overflow-like Q&A System

Requirements: Questions, answers, votes, users.

  • Key Classes: Forum, Question, Answer, User.
  • Patterns: Composite (thread structure).
  • SOLID: Single Responsibility (voting handler). Solution: Ranking by votes; moderation queue.

13. Design a Logging Mechanism

Requirements: Levels (info/error), appenders (file/console).

  • Key Classes: Logger (Singleton), Appender, LogMessage.
  • Patterns: Chain of Responsibility (level filtering).
  • SOLID: Dependency Inversion (appenders injectable). Solution: Asynchronous logging to avoid bottlenecks.

14. Design a Customer Support System

Requirements: Issues, agents, assignment strategies.

  • Key Classes: SupportSystem, Issue, Agent, AssignStrategy.
  • Patterns: Strategy (round-robin/expertise-based).
  • SOLID: Open-Closed (new strategies). Solution: Observer for updates; priority queues for issues.

15. Design an Inventory Management System

Requirements: Products, stock, orders, suppliers.

  • Key Classes: Inventory, Product, Order, Supplier.
  • Patterns: Observer (low stock alerts).
  • SOLID: Interface Segregation (read/write access). Solution: Real-time updates; reorder thresholds.

16. Design a Meeting Room Booking System

Requirements: Rooms, slots, users, conflicts.

  • Key Classes: Scheduler, Room, Booking, User.
  • Patterns: Facade (booking interface).
  • SOLID: Single Responsibility (conflict checker). Solution: Calendar integration; recurring bookings.
8. Design a Library Management System Requirements: Books, members, borrow/return, fines. Key Classes: Library, Book, Member, Loan. Patterns: Observer (overdue notifications). SOLID: Dependency Inversion (database interface). Solution: Track due dates; calculate fines daily. 9. Design a Car Rental System Requirements: Vehicles, reservations, users, payments. Key Classes: RentalSystem, Vehicle, Reservation, User. Patterns: Factory (vehicle types). SOLID: Interface Segregation (user/admin views). Solution: Availability calendar; integrate with maps for locations. 10. Design a Chess Game Requirements: Board, pieces, moves, rules. Key Classes: Game, Board, Piece (abstract), Player. Patterns: Flyweight (shared piece types). SOLID: Liskov (pieces extend base). Solution: Validate moves; detect checkmate with recursion. 11. Design a Splitwise-like Expense Sharing System Requirements: Groups, expenses, settlements. Key Classes: User, Group, Expense, SplitStrategy. Patterns: Strategy (equal/unequal splits). SOLID: Open-Closed (new split types). Solution: Graph for debts; simplify settlements. 12. Design a Stack Overflow-like Q&A System Requirements: Questions, answers, votes, users. Key Classes: Forum, Question, Answer, User. Patterns: Composite (thread structure). SOLID: Single Responsibility (voting handler). Solution: Ranking by votes; moderation queue. 13. Design a Logging Mechanism Requirements: Levels (info/error), appenders (file/console). Key Classes: Logger (Singleton), Appender, LogMessage. Patterns: Chain of Responsibility (level filtering). SOLID: Dependency Inversion (appenders injectable). Solution: Asynchronous logging to avoid bottlenecks. 14. Design a Customer Support System Requirements: Issues, agents, assignment strategies. Key Classes: SupportSystem, Issue, Agent, AssignStrategy. Patterns: Strategy (round-robin/expertise-based). SOLID: Open-Closed (new strategies). Solution: Observer for updates; priority queues for issues. 15. Design an Inventory Management System Requirements: Products, stock, orders, suppliers. Key Classes: Inventory, Product, Order, Supplier. Patterns: Observer (low stock alerts). SOLID: Interface Segregation (read/write access). Solution: Real-time updates; reorder thresholds. 16. Design a Meeting Room Booking System Requirements: Rooms, slots, users, conflicts. Key Classes: Scheduler, Room, Booking, User. Patterns: Facade (booking interface). SOLID: Single Responsibility (conflict checker). Solution: Calendar integration; recurring bookings.

17. Design a Restaurant Management System

Requirements: Tables, orders, menu, payments.

  • Key Classes: Restaurant, Table, Order, MenuItem.
  • Patterns: Builder (order customization).
  • SOLID: Liskov (payment methods). Solution: Table status; kitchen queue.

18. Design a Traffic Light System

Requirements: Intersections, lights, timers.

  • Key Classes: TrafficSystem, Light, Intersection.
  • Patterns: State (red/green/yellow).
  • SOLID: Dependency Inversion (timer interface). Solution: Synchronize lights; pedestrian modes.

19. Design a Deck of Cards

Requirements: Suits, ranks, shuffle, deal.

  • Key Classes: Deck, Card, Suit, Rank.
  • Patterns: Builder (deck creation).
  • SOLID: Open-Closed (add jokers). Solution: Random shuffle; deal hands.

20. Design an LRU Cache

Requirements: Capacity, get/put, eviction.

  • Key Classes: LRUCache, Node (doubly linked).
  • Patterns: (Custom implementation).
  • SOLID: Single Responsibility (eviction policy). Solution: HashMap + DLL for O(1) operations.

21. Design a Rate Limiter

Requirements: Requests per time window.

  • Key Classes: RateLimiter, TokenBucket.
  • Patterns: Strategy (algorithms).
  • SOLID: Interface Segregation. Solution: Token bucket for bursts; sliding window for precision.

22. Design a Notification System

Requirements: Users, channels (email/SMS), templates.

  • Key Classes: NotificationService, User, Channel.
  • Patterns: Observer (subscribers).
  • SOLID: Dependency Inversion. Solution: Queue for async delivery; retries.

23. Design a File System

Requirements: Directories, files, permissions.

  • Key Classes: FileSystem, Directory, File.
  • Patterns: Composite (tree structure).
  • SOLID: Liskov (files/dirs as nodes). Solution: Path resolution; CRUD operations.

24. Design a Hotel Management System

Requirements: Rooms, bookings, guests.

  • Key Classes: Hotel, Room, Booking, Guest.
  • Patterns: Factory (room types).
  • SOLID: Open-Closed. Solution: Availability search; check-in/out.

25. Design an Online Shopping Cart

Requirements: Items, quantities, checkout.

  • Key Classes: Cart, Item, User.
  • Patterns: Singleton (session cart).
  • SOLID: Single Responsibility. Solution: Persistent storage; discounts.

26. Design a Social Media Feed

Requirements: Posts, users, timelines.

  • Key Classes: FeedService, Post, User.
  • Patterns: Strategy (sorting algorithms).
  • SOLID: Interface Segregation. Solution: Fan-out for writes; caching.

27. Design a Cab Booking System (like Uber)

Requirements: Riders, drivers, trips.

  • Key Classes: CabService, Rider, Driver, Trip.
  • Patterns: Observer (location updates).
  • SOLID: Dependency Inversion. Solution: Matching algorithm; ETA calculation.

28. Design a Collaborative Editor (like Google Docs)

Requirements: Real-time edits, users.

  • Key Classes: Editor, Document, User.
  • Patterns: Observer (changes).
  • SOLID: Open-Closed. Solution: Operational transformation for conflicts.

29. Design a Weather Forecasting App

Requirements: Locations, data sources, updates.

  • Key Classes: WeatherService, Location, Forecast.
  • Patterns: Facade (API integration).
  • SOLID: Single Responsibility. Solution: Caching; periodic refreshes.

30. Design a Task Scheduling System

Requirements: Tasks, priorities, deadlines.

  • Key Classes: Scheduler, Task, PriorityQueue.
  • Patterns: Command (tasks).
  • SOLID: Liskov. Solution: Cron-like; handle dependencies.
30. Design a Task Scheduling System

These solutions emphasize extensibility—e.g., adding features without breaking code. Practice coding them fully!

Tips for Acing LLD Interviews

Engage your interviewer: Ask clarifying questions like “What are the key features?” or “Any scalability concerns?”

Common pitfalls: Don’t force patterns; justify choices. Time management—spend 10 mins on requirements, 20 on design, 10 on code.

Call to action: Practice these questions, then tackle our crash course for timed simulations. Share your experiences in the comments—what’s your toughest LLD question?

FAQs

What are common low-level design patterns for interviews?

Common patterns include Singleton for unique instances, Factory for object creation, and Strategy for algorithms—essential for modular code in LLD problems.

Start with requirements, identify classes (e.g., Spot, Vehicle), apply SOLID principles, and use patterns like Strategy for fee calculation.

What SOLID principles apply in LLD interview solutions?

SOLID ensures maintainable designs: Single Responsibility for focused classes, Open-Closed for extensions, and more in object-oriented low-level design.

FAANG often asks for systems like vending machines, elevators, or caches, testing design patterns, UML, and real-world extensibility.

How to prepare for machine coding in LLD rounds?

Practice coding full solutions to LLD problems, focus on clean code, design patterns, and explain trade-offs for better interview performance

DSA, High & Low Level System Designs

  • video-camera 85+ Live Classes & Recordings
  • 24*7 Live Doubt Support
  • 400+ DSA Practice Questions
  • Comprehensive Notes
  • HackerRank Tests & Quizzes
  • screen-users Topic-wise Quizzes
  • Case Studies
  • Access to Global Peer Community

Buy for 60% OFF
₹25,000.00 ₹9,999.00

Learn More
Got Confusion ?

Accelerate your Path to a Product based Career

Boost your career or get hired at top product-based companies by joining our expertly crafted courses. Gain practical skills and real-world knowledge to help you succeed.

Data Analytics

  • video-camera 120+ Live Classes & Recordings
  • 24*7 Live Doubt Support
  • 400+ DSA Practice Questions
  • Comprehensive Notes
  • HackerRank Tests & Quizzes
  • screen-users 12+ live Projects & Deployments
  • Case Studies
  • Access to Global Peer Community

Buy for 50% OFF
₹20,000.00 ₹9,999.00

Learn More

Low & High Level System Design

  • video-camera 20+ Live Classes & Recordings
  • 24*7 Live Doubt Support
  • Case Studies
  • Comprehensive Notes
  • HackerRank Tests
  • screen-users Topic-wise Quizzes
  • Access to Global Peer Community
  • Interview Prep Material

Buy for 65% OFF
₹20,000.00 ₹6,999.00

Learn More

Fast-Track to Full Spectrum Software Engineering

  • video-camera 120+ Live Classes & Recordings
  • 24*7 Live Doubt Support
  • 400+ DSA Practice Questions
  • Comprehensive Notes
  • HackerRank Tests & Quizzes
  • screen-users 12+ live Projects & Deployments
  • Case Studies
  • Access to Global Peer Community

Buy for 57% OFF
₹35,000.00 ₹14,999.00

Learn More

DSA, High & Low Level System Designs

  • video-camera 85+ Live Classes & Recordings
  • 24*7 Live Doubt Support
  • 400+ DSA Practice Questions
  • Comprehensive Notes
  • HackerRank Tests & Quizzes
  • screen-users Topic-wise Quizzes
  • Case Studies
  • Access to Global Peer Community

Buy for 60% OFF
₹25,000.00 ₹9,999.00

Learn More

Design Patterns Bootcamp

  • video-camera Live Classes & Recordings
  • 24/7 Live Doubt Support
  • Practice Questions
  • Case Studies
  • Access to Global Peer Community
  • screen-users Topic wise Quizzes
  • Referrals
  • Certificate of Completion

Buy for 50% OFF
₹2,000.00 ₹999.00

Learn More

LLD Bootcamp

  • video-camera 7+ Live Classes & Recordings
  • Practice Questions
  • 24/7 Live Doubt Support
  • Case Studies
  • Topic wise Quizzes
  • screen-users Access to Global Peer Community
  • Certificate of Completion
  • Referrals

Buy for 50% OFF
₹2,000.00 ₹999.00

Learn More
Explore our flagship courses

Reach Out Now

If you have any queries, please fill out this form. We will surely reach out to you.

Contact Email

Reach us at the following email address.

arun@getsdeready.com

Phone Number

You can reach us by phone as well.

+91-97737 28034

Our Location

Rohini, Sector-3, Delhi-110085

Get SDE Ready

Learning often happens in classrooms
but it doesn’t have to.

+91-9773728034
support@getsdeready.com
WhatsApp Icon
close menu icon

Master Your Interviews with Our Free Roadmap!

close menu icon

Hi Instagram Fam!
Get a FREE Cheat Sheet on System Design.

close menu icon

Hi LinkedIn Fam!
Get a FREE Cheat Sheet on System Design

close menu icon

Loved Our YouTube Videos? Get a FREE Cheat Sheet on System Design.